The spread of auditory masking effects in both the time and frequency domains are examined in several tonal masking studies. Simultaneous and non-simultaneous masking paradigms are used to map masked audiograms (or masking patterns) in which signal threshold is measured as a function of the frequency separation between signal and masker. In simultaneous masking, a brief tonal signal is added to either a continuous sinusoid or a gated sinusoid. By varying the duration of the masker, we hope to determine how long it takes for the gated sinusoid to reach steady-state effectiveness. Preliminary work shows that two perceptual phenomena are related to a steady-state masker: (1) emergence of aural combination tones and (2) extremely broad masking patterns. These phenomena may be related to the development of inhibitory processes underlying "edge effects" observed at the spectral peaks of a complex masker. The build-up of combination tones will be investigated in a study of transient masking effects produced by two-tone maskers. Under steady-state conditions, two-tone maskers have been shown to produce large masking effects at low-frequency loci by virtue of generation of low-frequency combination tones. The function relating level of an externally-generated tone required to produce masking equivalent to that produced by a combination tone and delay of the signal will provide information on the formation of combination tones. Masking patterns produced by leading and trailing sinusoidal maskers will be measured in a temporal masking experiment. A comparison of the spread of masking as a function of the temporal interval between signal and masker and duration of the masker should provide additional information on the development sharpening mechanisms in audition.